resolve vars in node substs

Author: lcnr

compiler/rustc_infer/src/infer/error_reporting/need_type_info.rs

@@ -692,6 +692,11 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
         }
     }
 
+    fn node_substs_opt(&self, hir_id: HirId) -> Option<SubstsRef<'tcx>> {
+        let substs = self.typeck_results.node_substs_opt(hir_id);
+        self.infcx.resolve_vars_if_possible(substs)
+    }
+
     fn opt_node_type(&self, hir_id: HirId) -> Option<Ty<'tcx>> {
         let ty = self.typeck_results.node_type_opt(hir_id);
         self.infcx.resolve_vars_if_possible(ty)
@@ -774,7 +779,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
         let tcx = self.infcx.tcx;
         match expr.kind {
             hir::ExprKind::Path(ref path) => {
-                if let Some(substs) = self.typeck_results.node_substs_opt(expr.hir_id) {
+                if let Some(substs) = self.node_substs_opt(expr.hir_id) {
                     return self.path_inferred_subst_iter(expr.hir_id, substs, path);
                 }
             }
@@ -802,7 +807,7 @@ impl<'a, 'tcx> FindInferSourceVisitor<'a, 'tcx> {
                         if generics.has_impl_trait() {
                             None?
                         }
-                        let substs = self.typeck_results.node_substs_opt(expr.hir_id)?;
+                        let substs = self.node_substs_opt(expr.hir_id)?;
                         let span = tcx.hir().span(segment.hir_id?);
                         let insert_span = segment.ident.span.shrink_to_hi().with_hi(span.hi());
                         InsertableGenericArgs {
@@ -1074,7 +1079,7 @@ impl<'a, 'tcx> Visitor<'tcx> for FindInferSourceVisitor<'a, 'tcx> {
             .any(|generics| generics.has_impl_trait())
         };
         if let ExprKind::MethodCall(path, args, span) = expr.kind
-            && let Some(substs) = self.typeck_results.node_substs_opt(expr.hir_id)
+            && let Some(substs) = self.node_substs_opt(expr.hir_id)
             && substs.iter().any(|arg| self.generic_arg_contains_target(arg))
             && let Some(def_id) = self.typeck_results.type_dependent_def_id(expr.hir_id)
             && self.infcx.tcx.trait_of_item(def_id).is_some()

src/test/ui/inference/ambiguous_type_parameter.stderr

@@ -2,7 +2,12 @@ error[E0282]: type annotations needed
   --> $DIR/ambiguous_type_parameter.rs:16:19
    |
 LL |     InMemoryStore.get_raw(&String::default());
-   |                   ^^^^^^^ cannot infer type for type parameter `K`
+   |                   ^^^^^^^
+   |
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     <InMemoryStore as Store<String, HashMap<K, String>>>::get_raw(&InMemoryStore, &String::default());
+   |     +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++             ~
 
 error: aborting due to previous error
 

src/test/ui/methods/method-ambig-one-trait-unknown-int-type.stderr

@@ -13,7 +13,7 @@ error[E0283]: type annotations needed
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:26:7
    |
 LL |     x.foo();
-   |       ^^^ cannot infer type for struct `Vec<_>`
+   |       ^^^
    |
 note: multiple `impl`s satisfying `Vec<_>: Foo` found
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:9:1
@@ -23,6 +23,10 @@ LL | impl Foo for Vec<usize> {
 ...
 LL | impl Foo for Vec<isize> {
    | ^^^^^^^^^^^^^^^^^^^^^^^
+help: try using a fully qualified path to specify the expected types
+   |
+LL |     <Vec<T> as Foo>::foo(&x);
+   |     ++++++++++++++++++++++ ~
 
 error[E0308]: mismatched types
   --> $DIR/method-ambig-one-trait-unknown-int-type.rs:33:20